This invention relates to control devices and methods for multicylinder internal combustion engines such as those of a automobile, etc., which are capable of discriminating a particular cylinder of the engine; more particularly, this invention relates to such control devices and methods which are capable of accomplishing cylinder discrimination at a low cost.
Internal combustion engines, in particular, those for automobiles, etc., generally comprise a plurality of cylinders, and are operated at four stroke cycles of suction, compression, explosion (combustion), and exhaust. For obtaining higher operation efficiency of these engines, it is important to control the ignition timing or the fuel injection timing to precise moments corresponding to particular crank angles. Thus, in recent years, the ignition timing of the igniter and the fuel injection timing sequence of the injector are usually controlled by a microcomputer. The microcomputer receives, in addition to various operating conditions, reference position signals of respective cylinders and a cylinder discriminating signal for distinguishing a particular cylinder, and thereby discriminates the operating positions of respective cylinders and controls the ignition timings, etc., to the precise moments.
FIG. 5 shows such a conventional control device for controlling the operation timings of the respective cylinders of a four-cylinder engine.
In FIG. 5, a crank shaft 1 and a cam shaft 4 are coupled via a timing belt 3, such that the cam shaft 2 rotates once for every two rotations of the crank shaft 1. The operation timings of the four cylinders No. 1 through 4, each provided with a power transistor 31, an ignition coil 32, and a spark plug 33, are displaced from each other by a half rotation (180 degrees) of the crank shaft, in the order indicated in the figure, such that for example, the operational timings of the cylinders No. 1 and No. 4 are displaced by 360 degrees from each other. A detector disk 5 for detecting the reference positions is coupled to the cam shaft 2 via a rotation shaft 4, to be rotated together therewith. The disk 5 is provided with four outer slits or windows 6, corresponding to the reference positions of respective cylinders, Nos. 1 through 4 and an inner window 7 for discriminating a particular cylinder (e.g., cylinder No. 1). On a fixing plate 8 are disposed a pair of photosensors 9 and 10 consisting of photocouplers.
The photosensor 9 detects the windows 6 and generates a reference position signal L1 consisting of a train of pulses representing the reference positions of the respective cylinders. The signal L1 is usually referred to by the acronym SGT. Each one of the pulses of L1 rises at the first reference position (75 degrees before top dead center, abbreviated to B75.degree.) and falls at the second reference position (5 degrees before top dead center, or B5.degree.) of one of the four cylinders No. 1 through No. 4 corresponding thereto. The photosensor 10 detects the window 7 and generates a cylinder discriminating signal L2 corresponding to the particular cylinder (e.g., cylinder No. 1). The signal L2, usually referred to by the acronym SGC, is outputted upon generation of those pulses of the signal L1 which correspond to the particular cylinder.
On the other hand, another reference position sensor 11, consisting of a proximity sensor or a reflection type photosensor, etc., is disposed at the crank shaft 1 to generate a reference position signal L once for every rotation of the crank shaft 1, for example.
The electrical control unit (ECU) 20 consisting of a microcomputer receives the signals L1, L2, and L, and controls, on the basis of the signals L1, and L2, for example, the ignition timings of respective cylinders, in the predetermined order No. 1, No. 3, No. 4, and No. 2, by turning on the power transistor 31 of respective ignition coils 32 so as to generate a spark across the ignition plug 33 of respective cylinders at the precise moment.
The electrical control unit 20 may control the ignition timings on the basis of the signal L from the position sensor 11. In this connection, it should be noted, as mentioned above, that the phases of the pair of cylinders No. 1 and No. 4 (or those of the pair of cylinders No. 3 and 2) are displaced by one rotation (360 degrees) of the crank shaft 1. Thus, when one of the pair of cylinders No. 1 and No. 4 (or No. 3 and No. 2) is in the compression stroke, the other of the pair is in the exhaust stroke. The reference position signal L generated by the sensor 11 at the crank shaft 1 corresponds to the reference positions of the pair of cylinders at the compression or the exhaust stroke. Thus, in the case where the microcomputer 20 utilizes only the reference signal L, it cannot discriminate between the two cylinders which are in the compression stroke and the exhaust stroke, respectively. Thus, in such case, the two cylinders No. 1 and No. 4 (or No. 3 and No. 2) which are in the compression and the exhaust stroke, respectively, are ignited simultaneously. There is no particular harm in igniting the cylinder in the exhaust stroke, since no explosion (combustion) takes place therein.
The control device for an internal combustion engine of FIG. 5, however, has the following disadvantage. For the purpose of discriminating the compression stroke of each one of the cylinders, it should be provided with a cylinder discriminating sensor 10 in addition to the reference position sensor 9. Thus, when a sensor system is adopted wherein the reference position sensor 11 is mounted at the crank shaft 1 while the cylinder discriminating sensor 10 is mounted at the cam shaft 2, the mounting structure of the sensor system becomes complicated and expensive. On the other hand, if the reference position sensor 11 alone is utilized in the control of the operational timing of cylinders, the two cylinders which are in the compression and the exhaust stroke, respectively, cannot be discriminated between, and hence spurious ignition currents are supplied to the cylinder in the exhaust stroke. This results in a useless dissipation of electric power.